This invention relates to the field of electromagnetically energized railguns and especially to hypervelocity high efficiency versions thereof.
Conventional chemical reactant or gun powder energized guns are considered to have an upper limit of muzzle velocity. One approach to achieving higher projectile velocities that are in excess of currently used values involves the use of the electromagnetically energized railgun. In order to achieve these higher velocity performances, however, railgun rail currents in the range of 250 kiloamperes to 4,000 kiloamperes (ka) are considered necessary along with energy storage arrangements measuring in the megajoule range.
Electromagnetic railguns are now considered for several defense and non-defense projectile launch applications which include earth-to-space launch transportation, hypervelocity aerothermodynamic investigations, lethality investigations and equation-of-state materials testing. These diverse applications translate to a broad range of railgun performance requirement, in which additional factors such as boresize, muzzle energy level, launch velocity, fire rate, barrel life, and systems size to mass ratio are a few of the additional salient characteristics to be considered.
Recent advances in the railgun art include barrels of lightweight and relatively stiff design, improved power supplies and energy switching arrangements, improved armature or projectile configurations, enhanced barrel materials, and low mass high "G" tolerant projectile packages. Functioning railgun embodiments employing plural of these advances in the art have been fabricated or are now being fabricated throughout the free world.
Notwithstanding these recent improvements in the railgun art, additional improvement is needed in at least four areas generally recognized as limitations to large scale usage of such apparatus. These improvements are especially needed in the areas of compact power supplies, improved rail life expectancy, hypervelocity projectile capabilities (velocities in the order of ten kilometers per second), and improved electrical energy to kinetic energy transformation efficiencies--efficiencies greater than 40%. The later two of these improvement areas are particularly addressed in the present invention.
The patent art includes several examples of railgun apparatus that is of general background interest with respect to the present state of the railgun art and the present invention. Included in these patents is the U.S. Pat. No. 4,938,113 of G. A. Kemeny et al which is concerned with an electromagnetic projectile launcher having reduced muzzle arcing. This arcing improvement is achieved through the use of a capacitor bank and lightning arrestor circuit which contribute to a current reversal sequence in the rails of the described railgun. Since the Kemeny apparatus does not include a nested primary rail portion, a ready distinction between the present invention and the Kemeny apparatus is apparent.
Another of these patents of background interest is U.S. Pat. No. 5,138,929 issued to W. F. Weldon et al. The Weldon et al patent contemplates the use of current guard plates surrounding the rails of a railgun in order to shape the railgun current waveforms into a more favorable distribution on the rails. In the Weldon apparatus the current flow in the surrounding guard plates interacts with rail currents to force a more uniform distribution of current across the entire rail surface and to thereby reduce peak current densities at the inside rail corners where heating is a problem. Since the Weldon et al apparatus does not contemplate the use of a segmented primary rail, a ready distinction with the present invention is apparent.
The patents of general interest also include U.S. Pat. No. 5,168,118 issued to J. M. Schroeder and concerned with the use of plural magnetic rings along a projectile accelerating barrel. In the Schroeder apparatus the natural or ringing frequency of the electrical current flowing in the coils of these magnetic rings is carefully adjusted to suit the velocity of the projectile being accelerated. Since the Schroeder apparatus employs discrete coils rather than the segmented rail and augmenting rail structures of the present invention a ready distinction for the present invention is discernible.
Also included in this art of general interest is U.S. Pat. No. 5,173,568 issued to J. F. Parmer and concerned with a magnetic gun apparatus in which superconducting dipoles are used to exclude certain magnetic fields from entering the gunbore. Since the Parmer apparatus does not include the segmented and nested rails of the present invention and since it also involves the use of superconducting elements, a number of distinctions exist between the present invention and the Parmer apparatus.
Additionally included in this patent art is U.S. Pat. No. 5,183,957 issued to W. F. Welden et al and concerned with an arrangement for controlling the distribution of current in the armature of a railgun by way of providing a low conductivity material dispersed along the rails. This material is preferably in the form of graphite or a graphite and copper mixture. Since the Welden et al '957 patent is also not concerned with segmented rails or augmenting rails a ready distinction is present with respect to the present invention.
Also of general background interest with respect to the present invention is the technical paper published by J. S. Kerrisk and titled "Current Distribution and Inductance For Rail-Gun-Conductors", LA-9092-MS, Los Alamos National Laboratory, November 1981. The Kerrisk paper is limited to a disclosure of current diffusion and inductance computations and therefore is of background and limited interest with respect to the combination invention herein disclosed. The Kerrisk paper is, however, incorporated by reference herein.